Large deposits of mineral trona in southwestern Wyoming near Green River Basin have been mechanically mined since the late 1940's and have been exploited by five separate mining operations over the intervening period. The nominal depth below surface of these mining operations ranges between approximately 800 feet to 2000 feet. All operations practiced some form of underground ore extraction using techniques adapted from the coal mining industry.
A variety of different systems and mining techniques (such as longwall mining, shortwall mining, solution mining, room-and-pillar mining, or various combinations) exist for mining ore from underground seams, such as trona seams. Longwall mining, shortwall mining, and room-and-pillar mining require miners and heavy machinery to be underground. Although any of these various mining techniques may be employed to mine trona ore, when a mechanical mining technique is used, it is preferably longwall mining.
A longwall mining system typically comprises a continuous mining machine used where extended portions or longwalls of seam are desired to be mined. Longwall mining includes mining parallel entries into the seam to be mined and connecting those entries with one or more primary passages. Such arrangement defines the longwall pillar(s) or panel(s) to be mined. Such longwall panels may, depending upon the seam configuration, extend 300-1,200 feet (ca. 100-400 m) for the width of the face to be mined and as high as a mile for the length of the panel to be mined. The roof of the primary passages is usually supported by movable roof supports during the mining of the exposed “face” of the longwall pillar.
Typical longwall mining techniques employ a mining machine that is known in the industry as a longwall “shearer”. The ore is cut from the mining face by the shearer. This machine typically can weigh from 75 to 120 tons and comprises a main frame, housing the electrical functions, tractive motive units to move the shearer along the face and pumping units (to power both hydraulic and water functions). The longwall shearer's mobile frame is generally elongated and is supported on floor-mounted tracks that are adjacent and substantially parallel to the mine face.
There are three main types of longwall shearers: double-ended ranging-drum shearer, single-ended ranging-drum shearer, and single-ended fixed-drum shearer, the double-ended ranging-drum shearer being the most common for trona mining.
For the double-ended ranging-drum shearer, at either end of the main shearer frame are fitted ranging arms which can be ranged vertically up down by means of hydraulic rams. A laterally-extending rotary-driven drum which is fitted with a plurality of mining cutting bits or teeth (e.g., 40-60 teeth) attached thereto is pivotally attached to each ranging arm. Within the ranging arms are housed very powerful electric motors (typically up to 1500 HP) which transfer their power through a series of gears within the frame and the arms to the drum mounting locations at the extreme ends of the ranging arms where the cutting drums are. The rotary-driven cutting drums are rotated at a speed of 20-50 revolutions per min to cut the ore from the seam.
Each rotary driven toothed drums supported on a ranging arm is brought into engagement with the mine face to dislodge ore material therefrom and cuts the ore face into pieces as the shearer frame is moved back and forth on the track in front of the mine face. The cut ore pieces fall into a face conveyor that is usually attached to the floor-mounted tracks and extends parallel to the longwall face. The face conveyor discharges the pieces of cut ore material onto other conveying systems to transport the material from the seam out of the mining area. As the mine face recedes, the roof support, the face conveyor, the track assembly, and the shearer are advanced toward the face to enable the shearer to continue mining.
The operation of the shearer is well known in the mining art and, as such, will not be discussed in detail herein. However, the skilled artisan will appreciate that as the shearer reaches the end of a longwall face, the cutting operation has to be turned around. In some instances, the entire shearer may have to be turned around for the ore face to be cut in both directions of travel. Or the height of the rotary arms needs to be adjusted. When the end of the panel is reached, the longwall mining operation has to be moved to another panel, and the shearer's cutting arms need to be removed from the shearer and reinstalled onto the shearer to start mining a new face.
In most commercial longwall shearers, the ranging arm is welded solid to a lifting bracket which is connected to the hydraulic ram. The welded system does not allow for the arm and brackets to be flipped and changed from a headgate arm to a tailgate arm. This means the ranging arm that is fit to run on one end of the shearer body cannot be moved to the other end of the shearer.
In other shearers, a removable cylindrical-shaped bushing with a single straight pin has been used to fasten the ranging arm to the lifting bracket when inserted into a cylindrical hole. This bushing has a welded cap on one end machined into the pin, and a bolted cap on the other end. This cylindrical-shaped bushing connecting the arm and bracket allows the easy removal of the shearer arm from the bracket and motor housing for maintenance and/or for longwall panel move. However the straight pin in the bushing often comes loose during longwall mining operation. This loose pin causes increased friction with surrounding parts due to its unintended movement, and as a result causes damage to the cylindrical hole into which the bushing is inserted. The cross-section of the hole can be deformed into an ovoid ‘egg’ shape, so that the bushing no longer fastens securely the ranging arm to the lifting bracket. The shearer ranging arm then vibrates and wobbles during mining operation requiring mining operation to stop in order for the bushing to be repetitively tightened. In some instances though, the vibrations/wobbling of the arm is such as to cause the bushing to fail completely or the pin to break.
Although this foregoing issue has been and will be described in terms of trona mining, it may also apply to any longwall mine from which a non-combustible ore (e.g., evaporite or metal/non-metal ore) or coal is extracted.
The present invention thus provides a remedy to some of the problems associated with past bushing designs and further can minimize downtime during longwall mining operation and/or during maintenance for shearer turn-around and/or during shearer move to a new ore panel.